1. Field of the Invention
The present invention relates to a damper used in the power transmission route of automobiles or the like, and more particularly to a structure suited to a damper located between a stepless speed change gear and an engine flywheel, in a power transmission route having a belt type stepless speed change gear.
2. Description of the Prior Art
In the damper disc located before the stepless speed change gear as mentioned above, it is required that the relative torsional stiffness of the input part and output part of the damper be low in the driving direction (rotating direction), and in other words it is required that the input part be twisted largely with respect to the output part at a relatively small torque. In such a disk, moreover, it is needed to maintain such low torsional stiffness until the torsional torque increases to a relatively large value (that is, in a wide torsional angle range).
To achieve such high torsional angle and low torsional stiffness, conventionally, in some of the discs, plural compression coil springs were arranged in series as the spring mechanism to be incorporated therein. However, in such structure using series type springs, the position or posture of the springs may be unstable due to effects of centrifugal force, and the spring contacts with its adjacent member, and due to effects of such contact friction, the torsional characteristic becomes unstable as the entire disc.
To solve such problems, for example, as disclosed in the Japanese Laid-open Patent 61-223349, an intermediate member is placed between the output member and the input member, and the spring is maintained in a stable state by this intermediate member.
In this published structure, however, a total of four intermediate members in two different kinds are used, and the number of parts is increased, and the structure becomes complicated. That is, in this disclosed structure, in the torsional action in the normal direction, the input member is engaged with a pair of first intermediate members to move in the same direction, and in the torsional action in the reverse direction, the input member is engaged with the other (second) pair of intermediate members to move in the same direction. Thus, in this structure, one pair of intermediate members to be engaged with the input member in the normal direction, and another pair of intermediate members to be engaged with the input member in the reverse direction are needed, and the structure is complicated.
It is hence a primary object of the invention to present a structure capable of solving the above problems.
More specifically, in the damper disc disposed before the stepless speed change gear, a low torsional stiffness is required in a wide torsional angle range particularly in the driving direction, and the invention is intended to present a damper disc in a simple structure by making use of this characteristic.